Some charting

First is the S&P500 percentage of the stocks above 200-days moving average:

As you can see that despite the market keeps making new highs this index peaked back in February and is quickly declining.

Second is the McClellan oscillator:

As you can see it peaked in December and is in decline.

The third is the NYSE advance-decline index:

It peaked in early June and is trending down.

So, no matter how you slice the whole market it is visible that it is driven up by fewer and fewer leaders while many companies are dropping out of the race. It is a market topping pattern, when money are more and more selective. When this happens the investor goal is to find out strong groups and keep them long and short those sectors that are already in decline trend.

Keep in mind that when the S&P500 finally start dropping the weak groups will drop even more, just because some sectors have to not suffer that much.